KR102761486B1 - Manufacturing line, process, and sintered article - Google Patents

Abstract

The manufacturing line includes a tape of green material guided through a furnace so that the furnace combusts an organic binder material and then partially sinters the tape without using a setter board. The sintered article resulting from the manufacturing line has a relatively large surface area, may be thin, and has a substantially unpolished state with few sintering-induced surface defects. Tension may be applied to the partially sintered tape as it passes through a second furnace of the manufacturing line to shape the resulting sintered article. The furnace is preferably oriented vertically and preferably operated continuously. Preferably, a ceramic material is used to form the tape.

Description

MANUFACTURING LINE, PROCESS, AND SINTERED ARTICLE

This application claims the benefit of priority under 35 U.S.C. §119 to U.S. Provisional Application No. 62/185,950, filed June 29, 2015, the entire contents of which are incorporated herein by reference.

Aspects of the present disclosure generally relate to a process for sintering a green tape, such as a green tape comprising polycrystalline ceramic grains bonded to an organic binder, as well as sintered articles, such as ceramic sheets or tapes, made by such a process.

Articles such as thin sheets, tapes, or ribbons of ceramics have many potential uses, such as acting as waveguides when the ceramic is transparent to light, or as substrates that can be coated or laminated to be incorporated into batteries and other components, or for other applications. Such articles can be manufactured by forming large ingots of sintered material, cutting slivers or plates of the material, and polishing the corresponding article to the desired shape and surface quality. Polishing helps to remove imperfections or defects from the surface of the article, but is time- and resource-consuming.

Such articles may also be manufactured by other processes including tape casting, gel casting, or sintering of green tape, such as strips of inorganic grains bound to an organic binder. The green tape is typically placed on a surface, called a setter board, and placed in a furnace where the organic binder is burned to sinter the inorganic grains. The setter board is typically formed of a refractory material that can withstand the sintering process. When the binder is removed, the setter board supports the tape.

The present inventors have observed that sintering causes the green tape to shrink, dragging portions of itself across the setter board during shrinkage. As a result, the supported side of the resulting sintered article has surface defects, such as drag grooves, sintering debris, impurity patches, etc., that are transferred from the refractory material of the setter board to the sintered article. FIGS. 1 and 2 illustrate examples of surface defects (112, 212) on sintered ceramic articles (110, 210), such as defects induced by the setter board during sintering. The inventors believe that such defects reduce the strength of each article by providing sites for stress concentration and crack initiation.

Additionally, when manufacturing increasingly thin sintered articles (e.g., sheets, tapes, ribbons), the applicants hypothesize that at some point the sintered article may become so thin that polishing becomes difficult, if not impossible. Thus, for such articles, one skilled in the art may not be able to remove surface defects induced by the setter board or by cutting during sintering. Similarly, for sintered articles that are still thin but are thicker, the applicants hypothesize that at some point the article has too much surface area for polishing. Control of conventional polishing equipment with thin sheets that are brittle and/or have a large surface area may become unwieldy and/or impractical. Thus, thin articles, especially articles having a relatively large surface area, having qualities generally associated with polishing, such as flatness, smoothness and/or a defect-free surface, may be obtained using conventional manufacturing methods and/or those skilled in the art may not attempt to manufacture such articles due to the strong disadvantages associated with overcoming the manufacturing challenges and the associated cost per article.

There is a need for equipment and a manufacturing process for manufacturing articles, such as sheets of polycrystalline ceramic, metal or other materials capable of being sintered, which articles can be manufactured efficiently, such as without excessive polishing, while also having excellent mechanical properties, such as due to having few surface defects. Such articles may be useful as substrates on printed circuit boards, in batteries, as cover sheets for displays, such as for handheld devices, or the articles may be useful in other ways.

The present inventors have discovered a technique for removing the setter board in the process of sintering a green tape, wherein the resulting sintered article may be unpolished but still have excellent mechanical properties. In some embodiments, the technique disclosed herein relates to a continuous manufacturing line, wherein the continuous tape comprises a green section comprising inorganic particles held together by an organic binder. In the manufacturing line, the green section is guided to a first heated location to combust or burn off the binder to form an unbonded section of the same tape. Next, along the manufacturing line, the unbonded section extends through a second heated location for at least partial sintering of the inorganic particles. The first and second heated locations may be heated by the same or different furnaces on the manufacturing line. If the tape is only partially sintered at the second heated location, an additional heated location, such as a third heated location to complete sintering of the tape, may be present on the manufacturing line to further process the tape. Partial sintering in the second heated position allows the tape to be tensioned for further sintering in the third heated position, where the tape remains flat, thereby facilitating particularly flat sintered sheets and/or having sintering-induced surface defects.

The foregoing is achieved in part by orienting the green tape past the second heated position in a manner that does not require setter board support for the green tape, such as orienting the tape vertically. Surprisingly, the applicants have found that even though the bonding agent in the tape has been burned or burned away, the weight of the tape below the unbonded section does not necessarily require cutting or separating the tape at the unbonded section before at least partial sintering occurs. The applicants have found that the tape can be maintained on its own long enough for at least partial sintering without the setter board. As a result, the sintered article is free of contact-induced surface defects that are typically created during sintering by the setter board. The surfaces on both sides of the sintered article are consistent with each other in terms of the number of defects, and the number is sufficiently low that the resulting sintered article has improved mechanical properties, such as increased tensile strength, compared to articles having more surface defects.

Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from the description or may be recognized by practicing the embodiments set forth in the detailed description, the claims, and the accompanying drawings. It is to be understood that both the foregoing general description and the following detailed description are exemplary only and are intended to provide an overview or framework for understanding the nature and character of the claims.

The accompanying drawings are included to aid further understanding and are incorporated into and constitute a part of this specification. The drawings illustrate one or more embodiments and, together with the description, serve to explain the principles and operation of various embodiments. As such, the present disclosure will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings.
Figures 1 and 2 are digital images of ceramic materials having surface defects.
Figure 3a is a schematic diagram of a manufacturing line according to an exemplary embodiment.
Figure 3b is a conceptual plot of temperature versus position along the manufacturing line of Figure 3a.
Figure 4 is a cross-sectional view of a furnace according to an exemplary embodiment.
Figure 5 is a digital image of a manufacturing line according to an exemplary embodiment of a tape being processed.
Figure 6a is a digital image of the unpolished surface of the sintered ceramic.
Figure 6b is a conceptual side profile of an unpolished sintered ceramic.
Figure 7a is a digital image of the polished surface of the sintered ceramic.
Figure 7b is a conceptual side profile of the polished sintered ceramic.
FIG. 8 is a perspective view of a sintered article in the form of a thin sintered tape of a material according to an exemplary embodiment.
Figure 9 is a schematic diagram from a side view of a manufacturing line according to another exemplary embodiment.
Figures 10 and 11 are perspective views of a manufacturing line according to other exemplary embodiments.
FIG. 12 is a schematic diagram of a manufacturing line or a portion thereof according to an exemplary embodiment.
FIG. 13 is a schematic diagram of a manufacturing line or a portion thereof according to another exemplary embodiment.
FIG. 14 is a schematic diagram of a manufacturing line or a portion thereof according to another exemplary embodiment.
Figure 15 is a micrograph of a thin ceramic sheet sintered on a setter board at 100x magnification.
Figure 16 is generally the same sheet as Figure 15 at a magnification of 500 times from within the dotted box illustrated in Figure 15.
Figure 17 compares partially and fully sintered tapes manufactured using the process of the present invention disclosed herein, with black letters superimposed on white paper.
Figure 18 compares partially and fully sintered tapes manufactured using the process of the present invention disclosed herein, with white letters superimposed on black paper.
FIG. 19 is a micrograph at 100x magnification of a thin ceramic sheet sintered using the process of the present invention disclosed herein.
The sheet in Fig. 20 is the same sheet as Fig. 19 at 500x magnification.
Figures 21 and 22 are surface scans of a tape according to an exemplary embodiment having widthwise (Figure 21) and lengthwise (Figure 22) height profiles.

Before referring to the following detailed description and drawings that illustrate exemplary embodiments in detail, it is to be understood that the present invention is not limited to the details or methods described in the detailed description or illustrated in the drawings. For example, as will be understood by those skilled in the art, features and properties associated with an embodiment depicted in one of the drawings or described in the text relating to one of the embodiments may be applied to other embodiments depicted in other drawings or described elsewhere in the text.

Referring to FIGS. 3A and 3B , a manufacturing line (310) includes a workpiece (e.g., a ribbon, tape, web, line, material), such as a tape (314), shown in a side view extending into a furnace system (312). The tape (314) may be routed around a bend or roller (316) and directed toward the furnace system (312). In an exemplary embodiment, the furnace system (312) includes a passageway (318) including a binder combustion location (B) and/or a sintering location (C) for at least partially sintering the tape (314) after it passes through the binder combustion location (B). In some embodiments, the binder combustion location (B) is adjacent to the sintering location (C), such as directly above or below the sintering location (C) along the manufacturing line (310), such as within 1 meter, within 50 centimeters, or within 10 centimeters. As will be further explained, the close arrangement of the binder combustion location B and the sintering location C reduces the time/length during which the tape (314) is unbonded by the binder prior to sintering.

According to an exemplary embodiment, the passage (318) of the furnace system (312) is oriented such that the tape (314) can extend generally vertically through the passage (318) without contacting a surface (320) of a section of the furnace system (312) intended for, for example, at least, combustion of the binder (e.g., at the binder combustion location (B)) and/or at least partial sintering of the tape (314) (e.g., at the sintering location (C)). For example, the passage (318) can be oriented such that the tape (314) extends generally vertically and moves upwardly and/or downwardly along a path that is oriented between 45 degrees and 135 degrees relative to horizontal, such as between 60 degrees and 120 degrees, for example, 90 degrees +/- 10 degrees. Passing the tape (314) through the binder combustion location (B) and/or the sintering location (C) without contacting the tape (314) with the surface (320) of the sintering location (C) and/or the surface (322) of the binder combustion location (B) is believed to improve the surface quality of the tape (314) when processed by the furnace system (312) by reducing material transfer through contact and/or scoring or other shaping of the tape (314).

In an exemplary embodiment, the first section of the tape (314) is a green tape section (314A) and may be positioned at location (A) along the manufacturing line (310). In an exemplary embodiment, the green tape section (314A) comprises a polycrystalline ceramic and/or mineral (e.g., alumina, zirconia, lithium garnet, spinel) bonded by an organic binder (e.g., polyvinyl butyral, dibutyl phthalate, polyalkyl carbonate, acrylic polymer, polyester, silicone, etc.). In contemplated embodiments, the green tape section (314A) may comprise metal particles bonded to the organic binder. In other contemplated embodiments, the green tape section (314A) may comprise glass grains (e.g., high purity silica grains, borosilicates, aluminosilicates, soda lime) or other inorganic grains bonded by the organic binder. In contemplated embodiments, the green tape section (314A) can include glass-ceramic particles (e.g., cordierite, LAS lithium aluminosilicate, Nasicon structured lithium metal phosphate, celsian) bound to an organic binder. According to exemplary embodiments, the green tape section (314A) has a pore size of from about 0.01 to about 25 volume %, and/or the inorganic particles have a median particle size diameter of from 50 to 1,000 nanometers and a Brunauer, Emmett and Teller (BET) surface area of from 2 to 30 m ² /g. In other contemplated embodiments, the aforementioned materials can be bound by the inorganic binder or other binders, and/or the aforementioned materials can be of different sizes or have different pores.

As the green tape section (314A) passes through the binder combustion location (B), the furnace system (312) is configured to combust and/or burn the binder material, e.g., a majority of the binder, e.g., at least 90% of the binder, from the green tape section (314A) due to oxidation, volatilization and/or cross-linking. According to an exemplary embodiment, the green tape section (314A) is self-supporting through the combustion location (B) and does not require and/or does not contact a surface (322) of the combustion location (B).

Beyond the binder burnout location (B), the tape (314) is no longer in a "green" state and a second section of the tape (314) is an unbonded tape section (314B) (e.g., a burned tape section, a burned binder tape section) which is unsintered but may be free of binder or may have burned binder. Since the unbonded tape section (314B) is in an operational state and/or lacks unburned binder, one skilled in the art would expect that the unbonded tape section (314B) could simply collapse or collapse under its own weight or the weight of portions of the tape (314) below the unbonded tape section (314B), for example, due to the lack of binder. However, the present applicant has discovered that if the tape (314) is properly handled, e.g., the tension of the tape (314) is controlled and/or the tape (314) is not flexed and/or reoriented prior to at least partial sintering of the inorganic material (e.g., ceramic grains) of the tape (314), the unbonded tape section (314B) can remain intact despite the bonding agent being combusted and/or burned off.

Still referring to FIG. 3A, the unbonded tape section (314B) portion of the tape (314) is then passed to and/or into a sintering location (C), wherein the furnace system (312) is configured to at least partially sinter the polycrystalline ceramic or other inorganic material of the unbonded tape section (314B). For example, the polycrystalline ceramic grains may be sintered such that the grains are bonded or fused to one another, yet the tape (314) still includes a significant amount of voids (e.g., at least 10 volume %, at least 30 volume %), where "voids" refers to the portion of the tape volume that is not occupied by the inorganic material, such as the polycrystalline ceramic.

Once at least partially sintered, the corresponding section of the tape (314) is an at least partially sintered tape section (314C). Partially, and not completely, sintering the at least partially sintered tape section (314C) increases the strength of the tape (314) to the extent that tension is applied to the tape (314) to facilitate subsequent forming of the tape (314). In an exemplary embodiment, under tension, additional sintering of the tape (314) occurs to produce a particularly flat or otherwise shaped sintered article (see generally FIG. 5 ).

In an exemplary embodiment, the manufacturing line (310) further includes a tension adjuster (324) that affects the tension of the tape (314), for example by directly interacting with the at least partially sintered tape section (314C). The tension adjuster (324) can control and separate the tension of the tape (314) above relative to below the tension adjuster (324) such that the tension can be different on the portion of the tape (314) on each side of the tension adjuster (324). In some embodiments, the tension adjuster (324) includes an air bearing that directs air along or against the direction in which the tape (314) moves through the manufacturing line (310) to, for example, adjust the tension of the tape (314). In other embodiments, the tension adjuster (324) includes a nip roller that pulls or pushes the tape (314) to affect the tension of the tape (314). In another embodiment, the tensioner (324) may be a wheel (e.g., see FIG. 12 ), wherein the friction on the surface of the wheel as well as the rotation of the wheel affects the tension of the tape (314). As described above, the tension of the tape (314) as it is sintered, for example at the sintering location (C) or other locations along the manufacturing line (310), may be used to shape the tape (314). Additionally, the tension (either positive or negative) applied to the tape (314) by the tensioner (324) may help hold together the unbonded tape sections (314B) by affecting the tension in that section.

Now, referring to FIG. 3B, the temperature of the tape (314) can vary along the length of the tape (314) as a function of the location of a particular portion of the tape (314) along the manufacturing line (310). Prior to entering the bonding burn location (B), the green tape section (314A) can experience a first temperature, such as room temperature (e.g., about 25 °C). Proximate the bonding burn location (B), the temperature experienced by the unbonded tape section (314B) of the tape (314) can be greater than the temperature experienced by the green tape section (314A), such as at least 200 °C, such as at least 400 °C. At and near the sintering location (C), the temperature experienced by the tape (314) can be greater than the temperature experienced by the tape (314) near the bonding burn location (B), such as at least 800 °C, such as at least 1000 °C at the sintering location (C). A portion of the tape (314) positioned along the manufacturing line (310) past the sintering location (C) may then experience a lower temperature than the portion of the tape (314) at the sintering location (C) and/or than the portion of the tape (314) at the binder combustion location (B), which experiences room temperature, for example.

Referring to FIG. 4, the furnace system (410) includes a guide (412) defining a passageway (414) extending at least partially through the furnace system (410), such as completely through a depth L1 of the furnace system (410). In some embodiments, the guide (412) may be a tube or shaft formed of a refractory material. In exemplary embodiments, the passageway (414) may be oriented generally vertically so that gravity acts in a straight line or in another manner along the length of an elongated workpiece (e.g., a flexible green tape, ribbon, line; see generally, tape (314) of FIG. 3A) and extends through the passageway (414). In some applications of the furnace system (410), the workpiece may be narrower than the passageway (414) and may be positioned within the passageway (414) so as not to contact a surface of the guide (412). The no system (410) can be used in a manufacturing line such as the manufacturing line (310).

In an exemplary embodiment, the passageway (414) of the furnace system (410) has a depth dimension (L1) extending through the furnace system (410), a width dimension (extending in and out of FIG. 4) orthogonal to the depth dimension (L1), and a gap dimension (L2) orthogonal to both the depth dimension (L1) and the width dimension. In an exemplary embodiment, the depth dimension (L1) of the passageway (414) is greater than the width dimension, which is greater than the gap dimension (L2). In an exemplary embodiment, the gap dimension (L2) is at least 1 millimeter, such as at least 2 millimeters, at least 5 millimeters, and/or 500 centimeters or less. In some embodiments, the width and gap dimensions are equal to each other such that the passageway (414) is cylindrical.

Referring to FIG. 4, the furnace system (410) includes a binder combustion location (B') and a sintering location (C'). The combustion location (B') is configured to combust binder material from the workpiece and the sintering location (C') is configured to at least partially sinter the workpiece. In an exemplary embodiment, the furnace system (410) includes a heat source (416), such as an electrical resistance heating element, a gas or oil burner, or other heat source. In some embodiments, the heat source (416) surrounds at least a portion of the sintering location (C') and/or is separated from the combustion location (B') by a barrier or wall (418), which may be formed of, for example, a refractory material. In an exemplary embodiment, the heat source (416) of the furnace system (410) is located above or below the combustion location (B'). Thus, heat can synergistically pass from the sintering location (C') to the binder combustion location (B'). In another embodiment, the combustion location (B) may have a heat source separate from the sintering location (C').

Before entering the binder combustion location (B'), the workpiece may experience a first temperature, such as room temperature (e.g., 25 °C). Near the binder combustion location (B'), the temperature experienced by the workpiece may be greater than room temperature, such as at least 200 °C, such as at least 400 °C. As the workpiece approaches and passes the sintering location (C'), the temperature experienced by the workpiece is still greater than the temperature experienced by the workpiece near the binder combustion location (B'), such as at least 800 °C, such as at least 1000 °C. A portion of the workpiece beyond the sintering location (C') on the side of the sintering location (C') opposite the binder combustion location (B') may then experience a lower temperature, such as experiencing room temperature.

Referring now to FIG. 5 , a cast of a 3 mole % yttria-stabilized zirconia (3YSZ) green ceramic can be fabricated, as described in U.S. Patent No. 8,894,920 . In one embodiment, a green tape (512) of material measuring 2.5 cm wide x 5 m long is cut from the cast. The green tape (512) is wound onto a cylindrical roller (514) and then fed at a controlled rate of 2 inches per minute into a furnace system (516) as shown in FIG. 5 (see also furnace system (410) as shown in FIG. 4 ). The sintering position (C") of the furnace system (516) is maintained at 1200 °C. The binder combustion position (B") is insulated and lined with alumina fiberboard to provide an area for binder combustion. The binder combustion location (B") was heated by the high temperature gas exiting the sintering location (C') of the furnace system (516).

In the illustrated configuration (510), the present inventors have found that a ten inch long binder combustion location (B") (illustrated in vertical length) allows the tape (512) to be successfully fed at up to about three inches per minute. The sintering location (C") of the illustrated furnace system (516) is twelve inches long, resulting in a total time at the sintering location (C") of about four to six minutes. At the exit of the furnace system (516), the 3YSZ tape (512') is partially sintered and has a relative density of about 0.65. The 3YSZ tape (512') is strong enough to handle, is flexible, and is about 40 micrometers thick. As illustrated in FIG. 5, several meters of the sintering tape (512') are reoriented onto a supporting plastic carrier film (518).

The present applicant has discovered that the binder combustion location (B") should be at a temperature in the range of about 200 to 600 °C for polyvinyl butyral (PVB) binders. The present applicant has discovered that a sufficient length of the binder combustion location (B") can also allow for high tape velocities through the furnace system (516), since if the binder combustion location (B") is too short, binder may be removed at an excessive rate, which may result in uncontrolled binder removal and destruction of the tape (512). Additionally, the present applicant has discovered that the length of the binder combustion location (B") is related to the rate at which the tape (512) can be successfully sintered. According to an exemplary embodiment, the length of the binder combustion location (B") is at least 2 inches and/or no more than 50 inches, such as at least 4 inches and/or no more than 20 inches. In other contemplated embodiments, the binder combustion location (B") can have a length outside the aforementioned ranges.

Continuing with reference to FIG. 5, in another example, a tape (512), this time an alumina green ceramic, is manufactured and fired using the composition (510). The process of casting the tape (512) includes the steps of batch processing, milling, degassing (or air removal), filtration, and tape manufacturing. For batch processing, an aqueous tape casting composition is mixed with alumina powder, including a binder, a dispersant, a plasticizer, and a defoaming agent. The composition used was produced by Polymer Innovations, including a water-soluble acrylic binder.

For milling, the batched material is milled and mixed in a mill, for example, by ball milling, high shear mixing, attrition milling, vibration milling, roller milling and similar methods. The milling step deagglomerates the particles to produce a uniform, well-dispersed slurry. In some embodiments, the applicants have discovered that an attrition mill (also referred to as an agitated ball mill) from Union Process can facilitate deagglomeration by breaking up agglomerates or nano-agglomerates of the alumina powder. The applicants believe that the attrition mill is advantageous over other milling processes and equipment due to the high energy input to the material during the milling process, which allows the batch to be milled to a smaller particle size in a shorter period of time, for example, 1 to 3 hours versus 50 to 100 hours of ball milling, as compared to other techniques.

A single Union Process abrasion mill was used having a total volume of 750 milliliters (mL) and a working volume/capacity of 250 mL. The tank was loaded with 130 mL of slurry and 740 grams of 2 mm 99.9% pure alumina media (i.e., grinding media). The tank was water cooled to 15 °C during the milling process to avoid overheating and to reduce evaporation of the solvent(s). The slurry was initially milled at 500 revolutions per minute (rpm) for 5 minutes to break up large agglomerates, then the speed was increased to 1300 rpm and milled for 1 hour. At the end of milling, the tank was slowed down to 170 rpm and a defoamer was added to remove entrapped air. The slurry was then poured through an 80 to 120 mesh screen to remove milling media from the slurry prior to degassing.

For example, for degassing after milling, the applicant has discovered that the milled media can be transformed from a slurry, and the slurry can be degassed/degassed using a vacuum to remove entrapped air from the milled product, which may otherwise contain air bubbles within the mixture. Degassing can be accomplished in the desiccant chamber, and then in the Mazerustar vacuum planetary mixer. The slurry can be loaded into the desiccant chamber and degassed for up to 10 minutes. After the initial degassing, the slurry can be loaded into the planetary mixer and operated under vacuum for 5 minutes. The applicant has discovered that an alternative degassing procedure that eliminates the Mazerustar mixer is to use a higher vacuum in the desiccant chamber.

For filtration, the slurry is filtered to remove any large contaminants from the mixture. Such contaminants may otherwise exhibit unfavorable optical properties in the sintered material, for example. Filtration may be accomplished with a 50 micrometer, 25 micrometer, 10 micrometer or 1 micrometer filter. Such filters may be made of, for example, nylon, fiber or other suitable materials.

For the tape fabrication step, the sample was cast onto a silicone coated Mylar® film having a thickness of about 50 to 150 micrometers. Applicants have found that the silicone coating provides easy peeling of the tape material after drying. Other suitable films for the tape (512) may be, for example, Teflon®, glass, metal belts, and similar alternative materials. To facilitate tape fabrication, the slurry was passed under a doctor blade having a gap of about 4 to 20 mils (about 100 to 500 micrometers) to form a thin sheet of ceramic tape. Typically, an 8 mil (about 200 micrometers) blade height was used. The casting blade was moved across the Mylar® at a speed of 10 mm/sec. The speed can be varied as needed to increase the processing speed and to vary the thickness of the tape (512). After drying, the tape had a thickness of 100 to 150 micrometers. The tape (512) in this state is referred to as a "green tape."

With continued reference to FIG. 5, a tape (512) measuring 1.2 meters long x 120 micrometers thick and 1.2 centimeters wide was cut and peeled from the green casting described above. The tape (512) was wound onto a cylindrical roller (514). The tape (512) was then fed into a furnace system (516) at a controlled rate of 1 inch per minute as illustrated in FIG. 5. The tape (512) had sufficient strength to hold itself together under its own weight during binder combustion. The sintering location (C") of the furnace system (516) was maintained at a temperature of 1100° C. At the exit of the furnace system (516), an alumina tape (512') having a relative density of about 0.7 was partially sintered. The sintered thickness of the tape (512') was about 100 micrometers.

Referring to FIGS. 6A and 6B , materials manufactured according to the process of the present invention and the equipment of the present invention disclosed herein can be distinguished from materials manufactured according to conventional processes. According to an exemplary embodiment, a sintered article (610) (e.g., a sheet, a foil) includes a first surface (612) (e.g., a top, a side) and a second surface (614) (e.g., a bottom) opposite the first surface (612). The sintered article further includes a body of material (616) extending between the first and second surfaces (612, 614).

The thickness (T) of the article (610) can be defined as the distance between the first and second surfaces (612, 614). The width of the article (610) (generally see the width (W) of the sintered sheet (810) of FIG. 8) can be defined as a first dimension of one of the first or second surfaces (612, 614) that is orthogonal to the thickness (T). The length of the article (610) (generally see the width (L) of the sintered sheet (810) of FIG. 8) can be defined as a second dimension of one of the first or second surfaces (612, 614) that is orthogonal to both the thickness (T) and the width. In an exemplary embodiment, the sintered article (610) is an elongated thin tape of sintered material. Due at least in part to their geometry, some such embodiments are flexible, allowing the article (610) to be bent around a mandrel or spool (e.g., 1 meter or less in diameter, 0.7 meters or less in diameter), which may be advantageous for manufacturing, storage, etc. In other embodiments, the sintered article (610) may be circular, annular, sleeve-shaped, tubular, or of variable thickness.

In an exemplary embodiment, the length of the article (610) is greater than twice the width of the article (610), for example, at least five times, at least ten times, or at least one hundred times greater. In some embodiments, the width of the article (610) is greater than twice the thickness (T) of the body, for example, at least five times, at least ten times, or at least one hundred times greater. In some embodiments, the width of the article (610) is at least 5 millimeters, for example, at least 10 mm, for example, at least 50 mm. In some embodiments, the thickness (T) of the article (610) is less than or equal to 2 centimeters, for example, less than or equal to 5 millimeters, for example, less than or equal to 2 millimeters, for example, less than or equal to 1 millimeter, for example, less than or equal to 500 micrometers, for example, less than or equal to 200 micrometers. In an exemplary embodiment, when the green tape is passed into the furnace and allowed to sinter, the sintering occurs substantially uniformly; The length, width and thickness of the sheet can be reduced by up to about 30%. Thus, the dimensions of the green tape disclosed herein can be up to 30% larger than those described for the sintered article described above. The thin tape allows the manufacturing line to operate quickly because heat from the furnace can quickly penetrate such tape and sinter it. Additionally, the thin tape can be flexible, facilitating bending and changing of direction along the manufacturing line (see, for example, generally FIG. 11 ).

According to an exemplary embodiment, the sintered article (610) is substantially unpolished such that either or both of the first and second surfaces (612, 614) have a granular profile, such as when viewed under a microscope, as illustrated in the digital image of FIG. 6A and conceptually illustrated in the side view of FIG. 6B . The granular profile includes grains (618) that protrude generally outwardly from the body (616) at boundaries (620) between grains (618) with a height (H) of at least 25 nanometers and/or 100 micrometers or less, for example, an average height of at least 50 nanometers and/or 80 micrometers or less. In other embodiments, the height (H) can be of a different size.

The granular profile is indicative of a process for manufacturing a sintered article (610) in that the article (610) is sintered as a thin tape, as opposed to being cut from a boule, and each surface (612, 614) is substantially unpolished. Furthermore, the granular profile may provide advantages to the sintered article (610) in some applications, such as increased surface area for scattering of light for a backlight unit of a display, greater adhesion of a coating, or culture growth, as compared to a polished surface. In contemplated embodiments, the unpolished surfaces (612, 614) have a roughness of from about 10 to about 1000 nanometers over a distance of 10 millimeters in one dimension along the length of the article, such as from about 15 to about 800 nanometers. In contemplated embodiments, one or both of the surfaces (612, 614) have a roughness of from about 1 nm to about 10 μm over a distance of 1 cm along a single axis.

In contrast, a sintered article (710) of the same material as the sintered article (610) includes a polished surface (712, 714), wherein grain boundaries are typically removed by polishing. In contemplated embodiments, a sintered article (610) manufactured according to the processes disclosed herein may be polished, as illustrated in FIGS. 7A-7B , depending on the particular intended use of the article. For example, use of the article (610) as a substrate may not require an extremely smooth surface, and the unpolished surface of FIGS. 6A-6B may suffice; whereas use of the article as a mirror or lens may require polishing, as illustrated in FIGS. 7A-7B . However, as disclosed herein, polishing can be difficult, particularly for thin articles or articles having a large surface area.

Applicants believe that, in contrast to the articles of FIGS. 6A-6B, sheets of sintered ceramic or other material cut from a boule may not have readily identifiable grain boundaries present on the surface. Additionally, Applicants believe that boule cut articles can typically be polished to correct rough surfaces from cutting. However, Applicants believe that surface polishing can be particularly difficult or tedious for very thin articles of sintered ceramic or other material, and that the difficulty increases as such articles become thinner and their surface areas increase. However, sintered articles made according to the presently disclosed technology are less constrained by this limitation, because articles made according to the present technology can be manufactured continuously as long lengths of tape. Furthermore, the dimensions of the furnace system as disclosed herein can be scaled to accommodate and sinter wider articles, such as those having a width of at least 2 centimeters, at least 5 centimeters, at least 10 centimeters, or at least 50 centimeters.

According to an exemplary embodiment, the sintered article (610) has a granular profile and a consistent surface quality on its surfaces (612, 614), which may be very different from an article manufactured using a setter board as described in the background art, where one side may be typically marked by contact from the setter board (e.g., adhesion and/or abrasion) while the other side may not be exposed to the setter board. In some embodiments, such as when the sintered article (610) is in the form of a sheet or tape (see generally sheet (810) as illustrated in FIG. 8 ), the surface consistency is such that the average area of surface defects per square centimeter of the first surface is within ±50 percent of the average area of surface defects per square centimeter of the second surface, for example, within ±30 percent of the average area of surface defects per square centimeter of the second surface, for example, within ±20 percent of the average area of surface defects per square centimeter of the second surface, wherein "surface defects" are wear and/or bond defects having a dimension along each of the surfaces of at least 15, 10, and/or 5 micrometers, as illustrated in FIGS. 1 and 2 .

According to an exemplary embodiment, the sintered article (610) has a high surface quality, which can also be very different from articles manufactured using setter boards as described in the background art, where adhesion and/or abrasion from the setter board can degrade the surface quality. In some embodiments, such as when the sintered article (610) is in the form of a sheet or a tape (see generally sheet (810) as illustrated in FIG. 8 ), the surface quality is such that both the first and second surfaces have less than 15, 10, and/or 5 surface defects having a dimension greater than 15, 10, and/or 5 micrometers on average per square centimeter, for example, less than 3 such defects on average per square centimeter, for example, less than 1 such defect on average per square centimeter. Thus, sintered articles manufactured according to the presently disclosed techniques can have relatively high and consistent surface quality. The present applicant believes that the high and consistent surface quality of the sintered article (610) facilitates increased strength of the article (610) by reducing the sites for stress concentration and/or crack initiation.

In an exemplary embodiment, the corresponding material of the article (610) and the grain of the green tape comprises a polycrystalline ceramic. In an exemplary embodiment, the article (610) can include (e.g., is, consists essentially of, or comprises at _least 50 wt % of) zirconia, alumina, spinel (e.g., MgAl ₂ O ₄ , ZnAl ₂ O ₄ , FeAl ₂ O ₄ , MnAl ₂ O ₄ , CuFe ₂ O ₄ , MgFe 2 O ₄ , FeCr ₂ O ₄ ), garnet, cordierite, mullite, perovskite, pyrochlore, silicon carbide, silicon nitride, boron carbide, titanium diboride, silicon alumina nitride, and/or aluminum oxynitride. In some embodiments, the article (610) is a metal. In another embodiment, the article (610) is glass sintered from powder grains. In some embodiments, the article (610) is IX glass and/or glass-ceramic. The materials disclosed herein may be composites.

Referring now to FIG. 8 , in some embodiments, the sintered article is in the form of a sheet (810) of a material disclosed herein (e.g., a sintered tape). The sheet (810) includes a surface (814) having an opposite surface thereon (e.g., a top or bottom) and a body extending between two surfaces (814) (generally, see side surfaces (612, 614) and body (616) of the article (610) of FIGS. 6A and 6B ). In an exemplary embodiment, the width (W) of the sheet (810) is defined as a first dimension of one of the surfaces (814) that is orthogonal to the thickness (T'). In an exemplary embodiment, the sheet (810) has at least two generally perpendicular longitudinal side edges (812). The length (L) of the sheet (810) is defined as a second dimension of one of the top or bottom surfaces (814) that is orthogonal to both the thickness (T') and the width (W). The length (L) can be greater than or equal to the width (W). The width (W) can be greater than or equal to the thickness (T').

In exemplary embodiments, the thickness (T') is less than or equal to 500 micrometers, such as less than or equal to 250 micrometers, such as less than or equal to 100 micrometers, and/or at least 20 nanometers. In exemplary embodiments, the sheet (810) has a surface area of at least 10 square centimeters, such as at least 30 square centimeters, such as at least 100 square centimeters, even greater than 1000, 5000, or in some embodiments even 10,000 square centimeters; or, for example, is sized in a different manner according to the geometry disclosed herein with respect to the embodiments of the article (610). In some embodiments, the sheet (810) has a width (W) that is less than 1/4, 1/5, 1/6, 1/7, 1/8, 1/9, 1/10, and/or 1/20 of its length (L). Such geometries may be particularly useful for certain applications, such as use of the sheet (810) as a substrate for a linear battery and/or use of the sheet (810) as a surface for growing carbon nanotubes in an oven, wherein the sheet (810) fills the surface of the oven but does not fill a significant volume of the oven.

In an exemplary embodiment, the sheet (810) comprises (e.g., is formed of, consists essentially of, or comprises more than 50 volume percent of) a material selected from the group consisting of polycrystalline ceramics and synthetic minerals. In other embodiments, the sheet (810) comprises glass, metal, or other materials as disclosed herein. Further, in an exemplary embodiment, the material of the sheet (810) is in a sintered form such that grains of the material are fused to one another (see generally, FIG. 6A ). The sheet (810) may have a granular profile (see generally, FIGS. 6A-6B ) or may be polished (see generally, FIGS. 7A-7B ).

For example, in some embodiments, the sheet (810) is manufactured from an alumina powder having a median particle size diameter of 50 to 1000 nanometers and a BET surface area of 2 to 30 m ² /g. The sheet (810) is manufactured from tape-cast alumina powder comprising 99.5 to 99.995 wt % alumina and about 100 to about 1000 parts per million (ppm) of a sintering additive, such as magnesium oxide. In some embodiments, the sheet (810) is translucent. When the sheet (810) has a thickness of 500 μm or less, the sheet (810) can have a total transmittance of at least 30% at a wavelength of about 300 nm to about 800 nm. In some embodiments, the total transmission through the sheet (810) is from about 50% to about 85% at wavelengths from about 300 nm to about 800 nm when the sheet (810) has a thickness of less than or equal to 500 μm. In some embodiments, the diffuse transmission through the sheet is from about 10% to about 60% at wavelengths from about 300 nm to about 800 nm when the sheet (810) has a thickness of less than or equal to 500 μm. In contemplated embodiments, the sheet (810) can have the transmission percentages described above at wavelengths in the aforementioned ranges, but at other thicknesses, such as those described herein. Materials described herein other than alumina can also result in such translucent sintered articles.

Referring to FIG. 9, the manufacturing line (910) includes a source (912) of green tape (922), a furnace system (914), tensioners (916, 918), and a receiver (920) of sintered tape (924). In an exemplary embodiment, the source (912) of green tape (922) may be in the form of a roll of green tape (922) that may be manufactured separately. From the source (912), the green tape (922) is guided into a first portion (926) of the furnace system (914), for example, through a guide passage (928). As illustrated in FIG. 9, in some embodiments, the green tape (922) is guided along a vertical axis through the furnace system (914) such that the green tape (922) does not contact the surface and/or the setter board of the furnace system (914).

The first portion (926) of the furnace system (914) can include a location for combustion of the binder (generally referenced as location B of the manufacturing line of FIG. 3) and a location for partial sintering of the tape (912) (generally referenced as location (C) of the manufacturing line of FIG. 3). Accordingly, the tape (932) exiting the first portion (926) of the first system (914) can be partially sintered. The tension of the tape (922) through the first portion (926) of the furnace system (914) can be affected by a tension regulator (916) that can differentiate the tension of the tapes (922, 932, 924) on each side of the tension regulator (916) along the manufacturing line (910). As illustrated in FIG. 9, below the tension regulator (916), the furnace system (914) includes a second portion (930).

In an exemplary embodiment, the tension in the tapes (932, 924) between the tension adjusters (916, 918) can be greater than the tension in the tapes (922, 932, 924) that are not between the tension adjusters (916, 918). In some embodiments, the increased tension between the tension adjusters (916, 918) can be used to keep the tape (932) flat as the tape (932) is sintered in the second portion (930) of the furnace system (914). As an example, the partially sintered tape (932) can be sufficiently flexible to bend and/or flatten due to the tension in the tape (932) between the tension adjusters (932, 918), yet sufficiently strong to support the tension without fracture of the partially sintered tape (932) due to the bonding of the partial sintering. In other words, in the second portion (930) of the furnace system (914), the partially sintered tape (932) is sintered to final density and held under tension sufficient to flatten the sheet, tape or ribbon, thereby eliminating curl, warp, camber, etc. that may occur in unconstrained sintering. As an example, the applicant has found that a 1 cm wide partially sintered ribbon of zirconia or alumina can support a tension of greater than 1 kg, or about 20 megapascals, without fracture.

Thus, referring back to FIG. 8, in the contemplated embodiment, the undeformed surface of the sheet (810) has a flatness of, for example, from about 0.1 μm to about 50 μm over a distance of 1 cm along a single axis along the length of the sheet (810). This flatness, combined with the surface quality, surface uniformity, large area, thin thickness, and/or material properties of the materials disclosed herein, may make the sheets, substrates, sintered tapes, articles, and the like particularly useful for a variety of applications, such as touch cover sheets for displays, high temperature substrates, flexible separators, and other applications.

Due to the limited ability of garnet to creep or relax under pressure loads, garnet can be difficult to reshape after it has been manufactured. Accordingly, garnet can be difficult to manufacture thin and flat by conventional processes. To this end, those skilled in the art have conventionally sandwiched a green body between flat refractory surfaces, which typically results in numerous surface defects on both sides of the sintered article. Accordingly, the presently disclosed technique is believed to be particularly useful for manufacturing thin sheets of synthetic garnet as disclosed herein.

Referring to FIG. 10, a manufacturing line (1010) similar to the manufacturing line (910) of FIG. 9 includes a source (1012) of green tape (1022), a furnace system (1014) having two separate portions (1026, 1030), a tensioner (1016, 1018), and a receiver (1020) of sintered tape (1024). However, in the manufacturing line (1010), the green tape is manufactured continuously on the line (1010). Additionally, the sintered tape (1024) is cut into strips (1032) (e.g., at least 5 centimeters long, at least 10 centimeters long, and/or less than 5 meters long, less than 3 meters long) as the sintered tape (1024) exits the second portion (1030) of the furnace system (1014). Subsequently, the strip (1032) can be laminated, packaged and transported.

Referring to FIG. 11, a manufacturing line (1110) includes a source (1112) of tape (e.g., green tape). The source is in the form of a spool (1114) of tape (1112), which is initially present on a polymer backing (1116), such as Mylar. As the tape (1112) is unwound from the spool (1114) generally horizontally (e.g., within 30 degrees of horizontal, within 10 degrees of horizontal), the polymer backing (1116) is pulled from the tape (1112) at a separation location (1118) and wound onto a separated spool (1120). Next, the tape (1112) passes over an air bearing (1122) and is gradually deflected with a controlled amount of sag toward a first guide (1124) which orients the tape (1112) generally in a vertical direction (e.g., within 30 degrees of the vertical, within 10 degrees of the vertical).

Following the first guide member (1124), the green tape (1112) moves upward to a first furnace (1126) (typically referring to furnace (410) as illustrated in FIG. 4). In some embodiments, the first furnace (1126) is a low-temperature furnace that burns or ignites an organic binder from the tape (1112) to form an unbonded section of the tape (1112). Additionally, the first furnace (1126) may partially sinter the resulting unbonded section of the tape (1112) to form a partially sintered section (1128) of the tape (1112). After passing through the first furnace, the tape (1112) may be guided through a second guide member (1130). The first and second guides (1124, 1130) align the tape (1112) with the passage through the first knives (1126) so that the tape (1112) does not contact the surface of the first knives (1126), thereby reducing the number of surface defects associated with adhesion and wear. Such tapes (1112) may still have some defects, for example, due to contact with floating particles, etc.

In an exemplary embodiment, following the second guide member (1130), the partially sintered section (1128) of the tape is routed over the wheel (1132). In some embodiments, the wheel (1132) has a low-friction surface (1134) over which the partially sintered section (1128) slides. A temperature difference between the wheel (1132) and the partially sintered section (1128) may help inhibit sticking or adhesion between the wheel (1132) and the partially sintered section (1128). In an exemplary embodiment, the wheel (1132) rotates to control the tension of the tape (1112), for example, by providing different tensions to the tape (1112) on either side of the wheel (1132).

For example, in some cases, the wheel (1132) rotates (e.g., clockwise) against the direction in which the tape (1112) slides over the wheel (1132) so that the tension in the tape (1112) on the side of the wheel (1132) from which the tape (1112) flows decreases, the tension in the tape (1112) on the side of the wheel (1132) along which the tape (1112) travels increases, and the increased tension is maintained at the end of the tape (1112) by a tension adjuster, such as a tape (1112) receiving spool (typically see FIGS. 3 and 9), a robot arm (typically see FIG. 10) pulling the tape (1112), a roller, etc. As the tape (1112) passes through a second, possibly higher temperature furnace (1136), the tension in the tape (1112) keeps the tape (1112) flat as the tape (1112) is fully sintered.

The configuration and arrangement of the manufacturing line, equipment, and resulting sintered articles as illustrated in the various exemplary embodiments are merely exemplary. While only a few embodiments have been described in detail in this disclosure, many modifications (e.g., changes in the size, dimensions, structure, shape, and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, and orientations) are possible without substantially departing from the novel teachings and advantages of the subject matter described herein. Some elements depicted as integrally formed may be composed of multiple parts or elements, the locations of elements may be reversed or otherwise varied, and the nature or number of discrete elements or positions may be changed or varied. The order or sequence of any process, logical algorithm, or method steps may be changed or rearranged according to alternative embodiments. Other substitutions, modifications, changes, and omissions may also be made in the design, operating conditions, and arrangement of the various exemplary embodiments without departing from the scope of the present teachings.

Referring again briefly to FIG. 6 , the granular profile includes grains (618) that protrude generally outwardly from the body (616) by a height (H) (e.g., an average height) at the boundaries (620) between grains (618) of at least 5 nanometers, such as at least 10 nanometers, such as at least 20 nanometers, such as at least 25 nanometers, and/or less than or equal to 200 micrometers, such as less than or equal to 100 micrometers, less than or equal to 80 micrometers, less than or equal to 50 micrometers relative to the concave portion of the surface.

Referring to FIG. 12, a manufacturing line (1210) for partial sintering includes a source of tape (1212) (e.g., green tape). The source is in the form of a spool (1214) of tape (1212), which is initially present on a polymer backing (1216), such as Mylar. In some such embodiments, the tape (1212) is pulled from the spool (1214) through a roller (1244) and a vacuum hug drum (1242), after which the polymer backing (1216) is pulled from the tape (1212) at a separation location (1218) and tensioned by a tensioning device (1240) over the roller (1246) and wound onto a separate spool (1220). The tape (1212) (without backing (1216)) passes into the bond combustion section (B'") of the furnace (1226). In some such embodiments, the tape (1212) enters without contacting the furnace (1226) and/or in a generally vertically oriented state.

Following the separation location (1218), the green shaped tape (1212) moves downward into the furnace (1226) (also see furnace (410) as generally illustrated in FIG. 4). In some embodiments, the binder combustion section (B'") of the furnace (1226) is a low temperature furnace that burns or combusts the organic binder from the tape (1212) to form an unbonded section of the tape (1212). A higher temperature portion (C'") of the furnace (1226) may also partially sinter the resulting unbonded section of the tape (1212) to form a partially sintered section (1228) of the tape (1212) as illustrated in FIG. 12 that passes out of the furnace (1226).

After passing through the knives (1226), the tape (1212) can be guided across a roller (1252) that acts as a second guide. The separation location (1218) and the exit roller (1252) can align the passage through the knives (1226) with the tape (1212) such that the tape (1212) does not contact the surface of the knives (1226), thereby reducing the number of surface defects associated with adhesion and wear. In an exemplary embodiment, the separation location (1218) and the roller (1252) or other guides at or near the exit of the knives (1226) are aligned substantially vertically along a line that is substantially perpendicular to one another, for example, within 15 degrees of the vertical, for example, within 10 degrees of the vertical.

The present applicant recognizes that such tape (1212) may still have some imperfections, such as due to contact with floating particles, airborne particles, etc. The exit roller (1252) may be made of a low friction polymer material. After passing through the exit roller (1252), the partially sintered tape may be wound onto a receiving spool (1250).

Example 1

A 90 foot long tape of partially sintered zirconia tape was generally manufactured with an apparatus as illustrated in FIG. 12. The green tape was manufactured using Tosho (Japan) zirconia powder 3YE in a manner similar to that described in U.S. Patent No. 8,894,920 B2. The green tape was cast to a width greater than about 20 cm and the green tape thickness was about 25 micrometers. The tape was then manually cut to a width of about 15 mm using a circular razor blade. The green tape passes from a draw spool (typically see spool (1214) of FIG. 12) over a separation location (see separation location (1218) of FIG. 12), through a combustion chimney (see combustion section (B'") of furnace (1226) of FIG. 12), through a transition zone (see section (X'") of FIG. 12), and into a high temperature furnace (e.g., section C'") of furnace (1226) of FIG. 12).

Referring to Example 1 in the context of FIG. 12, at the separation location (1218), the ceramic tape (1212) is separated from the carrier film (1216). The carrier film (1216) is moved through the tensioning device (1240) and onto the take-up spool (1220). The binder combustion zone (B'") is passively heated by hot air from the furnace section (C'"). The channels and binder combustion flue within the furnace used in Example 1 were fabricated from ceramic fiber board in parallel plates having a gap of 0.125 to 0.5 inches between the plates (typically see L2 and gap (414) of FIG. 4). The width of the channels perpendicular to the gap was about 3.5 inches. The length of the binder combustion zone was about 17 inches and the length of the furnace below the binder combustion zone was 24 inches.

Applicants recognize that the green tape may be threaded into the furnace at either low or high temperatures. For high temperature threading, Applicants have established a temperature in the vicinity of 1000° C. and a tape speed of 1 inch/minute for the furnace when sintering or partially sintering 3YSZ, 3 mol % yttria stabilized zirconia, tetragonal phase zirconia polycrystalline "TZP" and/or alumina or other ceramics having similar sintering temperatures. After the tape emerges from the bottom of the furnace after the high temperature threading, the temperature is increased and the tape speed is increased. For low temperature threading, Applicants recommend moving (i.e., conveying, returning) the tape while heating through the furnace at a low speed of 0.25 to 1 inch/minute.

In this Example 1, the tape was hot threaded, and after threading, the furnace was heated and set to 1200° C., and the tape was then moved through the furnace at a rate of 8 in./min. The binder combustion flue was at a temperature of about 100 to 400° C. The green tape was moved through the furnace for over 2.25 hours, resulting in a continuous length of partially sintered tape of about 90 feet.

The sintering shrinkage of the tape was approximately 9.5-10.5%. The partially sintered tape was rolled on a 3.25 inch diameter spool without cracking.

Example 2

A 65 foot length of partially sintered zirconia tape was fabricated in an apparatus similar to that illustrated in FIG. 12, and the green tape was fabricated in a manner similar to that described in U.S. Patent No. 8,894,920, also using Tosho (Japan) zirconia powder 3YE. The green tape was cast to a width greater than about 20 cm. The green tape had a thickness of about 25 micrometers. The green tape was then manually cut to a width of about 52 mm using a circular razor blade.

Next, the green tape was passed from the draw spool over the separation location and through the binder combustion flue, through the transition zone, and into a high temperature active heating furnace (e.g., furnace (1226)). The binder combustion zone was passively heated by heated air from the furnace. The channels within the furnace and the binder combustion flue were (re)made of ceramic fiber board with parallel plates having a gap of between 1/8 and 1/2 inches between the plates. The channel width was about 3 1/2 inches. The binder combustion zone was about 17 inches long and the furnace was 24 inches long.

In this Example 2, after threading, the furnace was heated to 1000°C, 1025°C, 1050°C, 1075°C, and 1100°C while moving the tape through it at a rate of 2 in./min. The binder combustion flue temperature was about 100 to 400°C. The tape was run at each temperature for about 1 hour. The furnace was operated for in excess of 6.5 hours, and a continuously partially sintered tape exceeding 65 feet (greens) was moved through the furnace.

The sintering shrinkage across the tape width was dependent on the furnace temperature, as listed in Table 1. Some out-of-plane deformation occurred, and the variation in sintering shrinkage in the table is partly due to out-of-plane deformation of the tape.

52 mm green tape temperature Shrinkage % 1000℃ 2.08% 1000℃ 1.56% 1025℃ 2.34% 1050℃ 3.47% 1075℃ 4.28% 1100℃ 5.61%

For example, in various embodiments disclosed herein, such as the materials and systems disclosed herein, the temperature of the high temperature furnace is at least 800 °C, for example at least 1000 °C. The green tap is passed at at least 1 inch/minute, for example at least 2 inches/minute. The rate can be increased by increasing the length of the furnace. The shrinkage of the green tape passing through it is at least 1.5%, in some embodiments at least 2%, and/or 20% or less, for example 15% or less.

Example 3

About 60 feet of partially sintered zirconia tape were fabricated in an apparatus similar to that illustrated in FIG. 12, and the green tape was fabricated in a manner similar to that described in U.S. Patent No. 8,894,920, also using Tosho (Japan) zirconia powder (3YE). The green tape was cast to a width greater than about 20 cm. The green tape was about 25 micrometers thick. The tape was then manually cut to a width of about 35 mm using a circular razor blade.

The green tape was passed from the draw spool over the separation point and through the binder combustion flue, through the transition zone and into the furnace. The binder combustion zone was passively heated by heated air from the furnace. The channels in the furnace and the binder combustion flue were made of ceramic fiber board with parallel plates having a gap of between 1/8 and 1/2 inches between the plates. The channel width was about 3 1/2 inches. The binder combustion zone was about 17 inches long and the furnace was 24 inches long.

In this Example 3, after threading, the furnace was heated to 1100 °C, 1150 °C, and 1200 °C while moving the tape at a rate of 4 to 6 inches per minute. The binder combustion flue was at a temperature of about 100 °C to 400 °C. At each temperature and each tape speed condition, about 10 feet of tape was spooled onto 3.25 diameter spools after partial sintering without destruction.

The sintering shrinkage was measured and listed in Table 2 below, where it is shown that some out-of-plane deformation occurred and the variation in sintering shrinkage in the table is partly due to out-of-plane deformation of the tape.

Temperature (℃) Speed (in/min) Shrinkage percentage 35 mm green width 1100 4 5.05 1100 6 5.16 1150 4 8.09 1150 6 6.73 1200 4 12.01 1200 6 11.20

Example 4

One hundred and seventy-five feet of partially sintered zirconia tape were manufactured in the apparatus illustrated in FIG. 12. Zirconia green tape was manufactured as described above, but the tape was manually cut to about 15 mm width using a circular razor blade. The tape was passed from the draw spool over a separation location and through a binder burner, through a transition zone, and into the furnace. Temperatures of 1100 °C to 1200 °C and speeds of 4, 6, or 8 inches per minute were operated. The binder burner had a temperature of about 100 °C to 400 °C and a total of 175 feet (green) of partially sintered tape was manufactured.

The sintering shrinkage was measured and listed in Table 3 below, where it is shown that some out-of-plane deformation occurred and the variation in sintering shrinkage in the table is partly due to out-of-plane deformation of the tape. When measured over 1200 mm along the length of the tape, the tape formed at 1200° C and 8 inches per minute had an overall average out-of-plane flatness over the length and width of the tape of about 0.6 mm.

Temperature (℃) Speed (IPM) Shrinkage percentage 15 mm green width 1100 4 5.38 1100 6 6.70 1100 8 5.07 1150 4 8.58 1150 6 8.16 1150 8 7.25 1200 4 11.89 1200 6 11.33 1200 8 10.07

Example 5

A 147 foot length of partially sintered zirconia tape was fabricated in an apparatus similar to that illustrated in FIG. 12. Zirconia green tape was fabricated as described above and manually cut to about 15 mm using a circular razor blade. The tape was processed as described above except that after threading, the furnace was heated to 1200 °C and the tape was moved at a rate of 8 in./min. The binder combustion flue was at a temperature of about 100 °C to 400 °C. The green tape was moved through the furnace over a period of 3 hours, and a continuous length (green) of partially sintered tape exceeding 147 feet was obtained.

Referring now to FIG. 13, a manufacturing line (1310) for partial sintering includes a source of partially sintered tape (1312). The source is in the form of a spool (1314) of partially sintered tape (1312), the tape (1312) may have an intercalating material. The tape (1312) is released from the spool (1314) and moves over a roller (1342). A plate (1346) of high temperature material forms a narrow channel in the furnace (1326).

Next, the tape (1212) passes into the groove (1326), the tape (1312) being generally vertical and/or not in contact with the groove and/or not in contact with the groove along its central portion. In contemplated embodiments, the edges of the tape may contact a guide or surface within the groove, but may be later removed as disclosed herein to provide a low-defect central portion of the tape. In some such embodiments, the longitudinal edges of the tape include cutting marks, such as mechanical marks or lasers.

After passing through the knurl (1326), the final sintered tape (1329) can be pulled across a tensioning device (1340). The input rollers (1342) and the tensioning device (1340) are generally aligned linearly with the channel through the knurl (1326) such that the tape (1312) does not contact the surface of the knurl (1326) in some embodiments, thereby reducing the incidence of adhesion and wear-related surface defects as described herein. After passing through the tensioning device (1340), the final sintered tape passes over two rollers (1344) and through a transport device (1360) (rollers, bearings, treads). After the transport device (1360), the final sintered tape can be spooled with or without an intermediary material.

In FIG. 14, a manufacturing line (1410) for partial sintering includes a source of partially sintered tape (1412). The source is in the form of a spool (1414) of partially sintered tape (1412), wherein the tape (1412) may have an intercalation material. As the tape (1412) exits the spool (1414), the tape (1212) then passes into a kiln (1426), wherein the tape (1412) is oriented generally vertically. A tensioner (e.g., a weight (1460), a roller) is attached to the partially sintered tape to pull the tape during sintering and/or keep the tape flat. In contemplated embodiments, the weight (1460) may be the length of the tape itself.

Surprisingly, as described above, the present inventors have found that short lengths of green tape with the binder burned out can support some tension without the tape falling off. The tensile strength of the section with the burned binder, however, prior to entering the high temperature furnace, is only a fraction of the tensile strength of an ideal fully sintered tape formed from green tape of the same material and of the same dimensions and composition, for example less than 20%, for example less than 10%, for example less than 5%, but still a positive value, for example at least 0.05%.

Example 6

A partially sintered tape of 15 mm (green) width was prepared as described in Example 1. A roll of this partially sintered tape of 15 mm (green) width and about 25 μm thickness (green) was then placed on an apparatus similar to the system (1310) illustrated in FIG. 13 (e.g., the second furnace, the second sintering location). The ceramic plates (1346) were made of silicon carbide. The gap between the plates was 2 to 8 mm and the width of the plates was 4 inches. The outer dimension of the furnace was 21 inches long. The furnace was heated to 1400 °C (e.g., at least 100 °C higher than the furnace of Example 1, such as at least 200 °C higher, such as 400 °C higher).

In Example 6, a partially sintered tape (Example 1) was manually rapidly threaded into a 1400° C. furnace at a speed exceeding 1 ft/min. Sufficient tape was provided from a spool (1314) and the tape (1312) was wound around a tensioning device (1340), through two rollers (1344) and through a transport device (1360).

After threading, the tape was moved at a speed of 2 inches per minute. A tension of less than 50 g was applied to the sintered tape by the tensioning device (1340). A dense final sintered tape of about 9 inches was produced (see, e.g., the fully sintered tape (2010) of FIGS. 17-22 ). If the tape is translucent, text can be read through the tape when placed in contact with the tape (see the fully sintered tape (2010) of FIGS. 17-18 , compare to the partially sintered tape (2012) of FIGS. 17-18 ). The tape exhibited a slight white haze from light scattering, possibly from some voids (e.g., less than 1 %, such as less than 0.5 % and/or at least 0.1 % voids).

The transverse shrinkage of the tape was approximately 24%. Batch processed material of the same type of tape casting has a sintering shrinkage of approximately 23% +/- approximately 0.5%. The partially sintered tapes used in these experiments had out-of-plane strain, but after final sintering the tapes were flat in the direction of tape movement. There was some "C-shaped" curl in the transverse direction of the web (tape). A 1 cm x 1 cm area of the fully sintered tape was examined under an optical microscope at 100X magnification. Both sides of the final sintered tape were examined. No adhesion or wear defects typical of setter boards were found.

As can be seen in Fig. 15, the final sintered tape can be bent to a radius of less than about 2.5 cm.

Example 7

A second-stage sintering apparatus similar to that illustrated in FIG. 14 was used. The furnace was only about 4 inches high and had a 2-inch hot zone. Partially sintered tape, 30 mm wide (green), manufactured in a manner similar to that described for Example 3 was used. Prior to partial sintering, the tape was about 25 micrometers thick. A spool of partially sintered tape was placed over the furnace to allow passage of the tape, and the furnace had narrow gaps of 3/16 inch and 3.5 inches wide at the top and bottom furnace insulation. The tape was cold-threaded through the gap and a 7.5 gram weight was attached (typically as shown in FIG. 14). The furnace was heated to 1450 °C, and tape motion was started when the furnace reached 1450 °C. The tape was moved from the top to the bottom at a rate of 0.5 inch per minute. Approximately 18 inches of fully sintered sintered zirconia tape was manufactured. The zirconia tape was translucent. In Example 7, at a 4-inch furnace, the tape and its fully sintered portion were longer than the furnace.

In FIGS. 15 and 16, for context and comparison purposes, a green tape (3 mol % yttria-stabilized zirconia) was manufactured as described in the examples above and sintered using a conventional sintering process including using an alumina setter board to support the green tape during sintering to form a ceramic tape (3010). As shown in FIG. 15 , surface defects due to adhesion and wear from the setter board can be seen at 100X magnification. Since the sheet is very thin, on the order of 25 micrometers, many of the defects due to adhesion or wear form pin holes in the sintered sheet. As shown in FIG. 15 , the defects due to adhesion and wear from the setter board are generally elongated in a common direction with one another.

As previously mentioned, setter-induced defects are surface features typically caused by sintering shrinkage of the green tape in contact with the setter board, whereby the ceramic drags a portion of itself across the setter board during the sintering shrinkage. As a result, the supported side of the resulting sintered article will have surface defects such as pits in the surface where the setter withdraws material from the sintered article, drag grooves, sintering debris, and impurity patches that are transferred from the refractory material of the setter board to the sintered article. Minimizing such setter defects is important when the ceramic article has a thin film deposited thereon. When the layer thickness of the thin film is similar to the setter defect dimensions, the thin film may have pin holes or setter defects that cross the thin film layer(s).

The ceramic tape (2010) of FIGS. 15-16 is compared to the ceramic tape (3010) of FIGS. 17-22, particularly FIGS. 19 and 20, having the same magnifications of 100x and 500x as FIGS. 15 and 16, formed from a green tape manufactured in the same manner as the tapes used for FIGS. 15 and 16. More specifically, as disclosed herein, the ceramic tape (2010) was continuously sintered and run at 1400° C. at a rate of 2 inches per minute through a secondary furnace as described in the examples having a silicon carbide central channel. Comparing the ceramic tape (3010) and the ceramic tape (2010), both tapes exhibit various casting marks on their surfaces, such as elongated rolling marks and bevels (hills/valleys). The ceramic tape (3010) exhibits a number of setter-related defects, such as bonding particles, pull-out, and setter-drag defects, as described herein, where setter drag creates a characteristic damage pattern in areas due to surface gouging as the shrinking tape is dragged across the setter surface.

Referring to FIGS. 15 and 16 and FIGS. 19 and 20, bound particles having cross-sectional dimensions greater than 5 μm were readily observed at 100x during optical inspection of the surface (see FIGS. 15 and 19 ). More specifically, over an area of about 8 cm ² , one such particle was observed on the surface of a ceramic tape (2010) sintered using the technique disclosed herein, and over an area of about 8 cm ² , eight such particles were observed on the surface of a ceramic tape (3010). Applicants believe that while the ceramic tape (2010) has fewer bound surface particles that may be present due to adhesion of the particles in the furnace atmosphere, the ceramic tape (3010) has more bound particles due to contact with the setter. This small number of bound surface particles on the ceramic tape (2010) may be further reduced in future process embodiments that utilize filters or other processes to remove or reduce the particles in the furnace atmosphere.

In an exemplary embodiment, a tape manufactured according to the present disclosure has, on average, less than 5 bound particles per 8 cm ² over its surface, each particle having a cross-sectional dimension of less than 5 μm, for example less than 3, for example less than 2.

In an exemplary embodiment, as disclosed herein, the sintered ceramic sheet has a thickness of less than 50 micrometers and less than 10 pin holes (or less than 10 pin openings over the entire surface if the surface area is less than a square micrometer) having a cross-sectional area of at least one square micrometer per square millimeter of surface on average over the entire surface, for example less than 5 pin holes per square millimeter of surface, less than 2 pin holes, or even less than 1 pin hole per square millimeter of surface on average over the entire surface.

As shown in FIGS. 19 and 20 , the ceramic tape (19) has a granular surface having protrusions (2014). The protrusions have a longest dimension of about 100 micrometers or more. The protrusions are generally elongated in shape and have their major axes generally oriented in the same direction as each other, for example, within 15 degrees of direction D, such as within 10 degrees. Since the protrusions generally roll smoothly and are continuously curved away from the adjacent surface, as opposed to being formed by or including discontinuous boundaries or breaks in the surface, as would be characteristic of wear or adhesion induced by the setter, the protrusions can be distinguished from setter-induced surface defects such as wear or adhesion. The protrusions may be indicative of at least some of the processes disclosed herein, such as those resulting from a less constrained sintering process. Other embodiments may not include such a raised portion, for example where the tape is tensioned in the axial and transverse directions during sintering, which tensioning may be accomplished by a tensioner (e.g., a roller, tread, wheel, mechanical tensioner or other such element).

Referring now to FIGS. 21 and 22, a ceramic tape (4010) was manufactured according to the process disclosed herein without a setter board. The material of the tape (4010) is 3 mole % yttria stabilized zirconia, tetragonal phase zirconia polycrystalline "TZP". The width of the tape is 12.8 to 12.9 mm. The portion depicted is obtained from a 22 inch long piece of tape. The thickness of the tape is about 22 micrometers. Also, the white dots are marker markings on the tape that were not recognized by the scanner.

For comparison, the tapes are fully sintered below the line and only partially sintered above the dashed line L. SEC1, SEC2, SEC3, and SEC4 are profiles of the top surfaces of the ceramic tapes (4010). The profiles show that the tapes have a slight “C-shaped” curvature about their longitudinal axis (shown as the X-axis in FIG. 21 ). The camber within the tapes is reduced by full sintering under tension, as disclosed herein. As can be seen, the maximum height of the tapes is reduced by about 100%, from about 1.68 mm to between 0.89 and 0.63 mm. The present applicant believes that the maximum height of a fully sintered tape lying flat on a flat surface can be reduced to less than 1.5 mm, for example less than 1 mm, for example less than 0.7 mm, for example ideally less than about 100 micrometers, for example for a tape having a width of about 10 to 15 mm, through current process and/or further process improvements, such as increased tension or changes in process speed.

In contemplated embodiments, the tape described herein can be wound on a spool as illustrated in the drawings to form a tape roll. The spool can have a diameter of at least about 0.5 cm, such as at least about 2.5 cm and/or less than 1 m, the tape can have a length of at least 1 m, such as at least 10 m, and a width and thickness as described herein and/or a width of at least 10 mm and/or less than 20 cm and a thickness of at least 10 μm and/or less than 500 μm, such as less than 250 micrometers, such as less than 100 micrometers, such as less than 50 micrometers.

Claims (17)

It is a sintered product,
A sintered article comprising a first surface, a second surface and a body of material extending therebetween, the second surface being opposite the first surface of the sintered article such that a thickness of the sintered article is defined by a distance between the first and second surfaces, a width of the sintered article being defined by a first dimension of one of the first or second surfaces being perpendicular to the thickness, and a length of the sintered article being defined by a second dimension of one of the first or second surfaces being perpendicular to both the thickness and the width of the sintered article,
The body of the material contains inorganic materials,
The length of the sintered article is greater than or equal to the width of the sintered article, the sintered article is thin so that the width of the sintered article is greater than five times the thickness of the sintered article, and the thickness of the sintered article is 1 millimeter or less.
The sintered article is substantially unpolished so that each of the first and second surfaces has a granular profile;
The sintered article has a high surface quality having an area of at least 1 square centimeter having less than 10 surface defects from adhesion or wear having a dimension greater than 5 micrometers on both the first and second surfaces, wherein the high surface quality aids the strength of the sintered article,
A sintered article having a consistent surface quality on both the first surface and the second surface such that the average area per square centimeter of surface defects from adhesion or abrasion having a dimension greater than 5 micrometers on the first surface is within +/- 50% of the average area per square centimeter of surface defects from adhesion or abrasion having a dimension greater than 5 micrometers on the second surface. A sintered article in accordance with claim 1, wherein the granular profile comprises grains having a height ranging from 25 nanometers to 150 micrometers with respect to the concave portions of the first and second surfaces at the boundaries between each grain. A sintered article in claim 1, wherein the article has a flatness in the range of 100 nanometers to 50 micrometers over a distance of 1 centimeter in the longitudinal direction along either the first surface or the second surface. A sintered article in claim 1, wherein in a substantially unpolished state, at least one of the first and second surfaces has a roughness in the range of 1 nanometer to 10 micrometers over a distance of 1 centimeter measured along a longitudinal profile along either the first or second surface. A sintered article, wherein the article is particularly thin and elongated, such that the length of the article is greater than five times the width of the article, and the width of the article is greater than ten times the thickness of the article, in the first paragraph. A sintered article in claim 5, wherein the thickness of the main body is less than 0.5 millimeters, and the area of one of the first and second surfaces is greater than 30 square centimeters. A sintered article in claim 6, wherein one of the first and second surfaces has an area greater than 100 square centimeters. A sintered article in claim 1, wherein the inorganic material is an inorganic material selected from the group consisting of polycrystalline ceramics and synthetic minerals. It is a sintered product,
The sintered article is a sheet comprising a first surface, a second surface and a body of material extending therebetween, the second surface being opposite the first surface of the sheet such that a thickness of the sheet is defined by a distance between the first and second surfaces, a width of the sheet is defined by a first dimension of one of the first or second surfaces that is perpendicular to the thickness, and a length of the sheet is defined by a second dimension of one of the first or second surfaces that is perpendicular to both the width and the thickness of the sheet,
The body of the material is made of a material selected from the group consisting of polycrystalline ceramics and synthetic minerals, and the material exists in a sintered form so that the grains of the material are fused to each other.
The first and second surfaces of the sheet are substantially unpolished, each having a granular profile comprising grains having a height in the range of 25 nanometers to 150 micrometers relative to the concave portion of each surface at the boundary between the grains,
The sheet is thin and elongated so that the length of the sheet is greater than five times the width of the sheet, the width of the sheet is greater than five times the thickness of the sheet, the thickness of the sheet is 1 millimeter or less, and the area of each of the first and second surfaces is greater than 10 square centimeters,
The sheet has a high surface quality, such that both the first surface and the second surface have an area of at least 10 square centimeters having less than 100 surface defects from adhesion or wear having a dimension greater than 5 micrometers,
A sintered article, wherein the sheet has a flatness in the range of 100 nanometers to 50 micrometers over a distance of 1 centimeter in the longitudinal direction along either the first surface or the second surface. In the 9th paragraph, in addition to a material selected from the group consisting of polycrystalline ceramics and synthetic minerals, a sintered article wherein the material of the body of the material is also a material selected from the group consisting of alumina, zirconia, spinel and garnet. A sintered article in claim 10, wherein the thickness of the sheet is 500 micrometers or less. A sintered article in claim 11, wherein the sheet is at least partially transparent and has a total transmittance of at least 30% at wavelengths from 300 nanometers to 800 nanometers. A sintered article in claim 10, wherein one of the first and second surfaces has an area greater than 100 square centimeters. A sintered article in claim 9, wherein in a substantially unpolished state, at least one of the first and second surfaces has a roughness in the range of 1 nanometer to 10 micrometers over a distance of 1 centimeter in the longitudinal direction along either the first or second surface. It is a sintered product,
The sintered product is a ceramic tape,
The ceramic tape comprises a first surface, a second surface and a body of material extending therebetween, the second surface being opposite the first surface of the ceramic tape such that a thickness of the ceramic tape is defined by a distance between the first and second surfaces, a width of the ceramic tape being defined by a first dimension of one of the first or second surfaces being perpendicular to the thickness, and a length of the ceramic tape being defined by a second dimension of one of the first or second surfaces being perpendicular to both the thickness and the width of the ceramic tape,
The body of the material is a ceramic selected from the group consisting of alumina and zirconia, and the material exists in a sintered form so that the grains of the material are fused together.
The first and second surfaces of the ceramic tape are substantially unpolished, each having a granular profile comprising grains having a height in the range of 10 nanometers to 150 micrometers relative to the concave portion of each surface at the boundary between the grains,
The ceramic tape is thin and elongated so that the length of the ceramic tape is greater than five times the width of the ceramic tape, the width of the ceramic tape is greater than five times the thickness of the ceramic tape, the thickness of the ceramic tape is 150 micrometers or less, and the area of each of the first and second surfaces is greater than 2 square centimeters,
The ceramic tape has a raised portion, at least some of the raised portions having a maximum surface dimension of between 100 micrometers and 1 mm, the raised portions having a smooth continuous curvature relative to the adjacent surrounding surface such that the boundaries of the raised portions are not generally characterized by adhesion and wear,
A sintered article, wherein when laid unrestrained on a flat surface, the ceramic tape has camber about an axis along the length of the ceramic tape. In claim 15, the camber is a sintered article which causes a high point of the ceramic tape on a flat surface to be at least 10 micrometers greater than the thickness of the tape, and not more than 1 millimeter. It is a roll of ceramic tape,
spool, and
Contains tape wound on a spool,
A roll of ceramic tape, wherein the ceramic tape is a sintered article as described in any one of claims 1 to 16, and the length of the ceramic tape is at least 1 meter.

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